U.S. patent application number 14/345568 was filed with the patent office on 2014-12-18 for method and apparatus for outer loop link adaptation for a wireless communication system.
This patent application is currently assigned to NEC (CHINA) CO., LTD.. The applicant listed for this patent is Qingwei Ge, Ming Lei, Zhennian Sun, Gang Wang. Invention is credited to Qingwei Ge, Ming Lei, Zhennian Sun, Gang Wang.
Application Number | 20140369283 14/345568 |
Document ID | / |
Family ID | 49258063 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140369283 |
Kind Code |
A1 |
Ge; Qingwei ; et
al. |
December 18, 2014 |
METHOD AND APPARATUS FOR OUTER LOOP LINK ADAPTATION FOR A WIRELESS
COMMUNICATION SYSTEM
Abstract
The present invention relates to a method for link adaptation in
a wireless communication system. The method comprises: determining
whether a UE operates in a SU-MIMO transmission mode or in a
MU-MIMO transmission mode; applying, in responsive to determination
that the UE operates in the SU-MIMO transmission mode, a SU-MIMO
OLLA offset to a signal to interference and noise ratio adjusted
with inner loop link adaptation; applying, in responsive to
determination that the UE operates in the MU-MIMO transmission
mode, a MU-MIMO OLLA offset to a signal to interference and noise
ratio adjusted with inner loop link adaptation, wherein the MU-MIMO
OLLA offset is based on the SU-MIMO OLLA offset and an extra offset
which is indicative of inter-user interference, wherein the SU-MIMO
OLLA offset and the extra offset are updated in responsive to
receipt of an ACK/NACK message for a packet reported from the
UE.
Inventors: |
Ge; Qingwei; (Beijing,
CN) ; Wang; Gang; (Beijing, CN) ; Sun;
Zhennian; (Beijing, CN) ; Lei; Ming; (Beijing,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ge; Qingwei
Wang; Gang
Sun; Zhennian
Lei; Ming |
Beijing
Beijing
Beijing
Beijing |
|
CN
CN
CN
CN |
|
|
Assignee: |
NEC (CHINA) CO., LTD.
Beijing
CN
|
Family ID: |
49258063 |
Appl. No.: |
14/345568 |
Filed: |
March 27, 2012 |
PCT Filed: |
March 27, 2012 |
PCT NO: |
PCT/CN2012/073118 |
371 Date: |
September 2, 2014 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04B 7/0689 20130101;
H04B 7/0413 20130101; H04L 1/1867 20130101; H04W 24/02 20130101;
H04B 7/0452 20130101; H04W 72/082 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 24/02 20060101
H04W024/02; H04W 72/08 20060101 H04W072/08 |
Claims
1. A method for link adaptation in a wireless communication system,
comprising: determining whether a UE operates in a SU-MIMO
transmission mode or in a MU-MIMO transmission mode; applying, in
responsive to determination that said UE operates in the SU-MIMO
transmission mode, a SU-MIMO OLLA offset to a signal to
interference and noise ratio adjusted with inner loop link
adaptation; applying, in responsive to determination that said UE
operates in the MU-MIMO transmission mode, a MU-MIMO OLLA offset to
a signal to interference and noise ratio adjusted with inner loop
link adaptation, wherein said MU-MIMO OLLA offset is based on said
SU-MIMO OLLA offset and an extra offset which is indicative of
inter-user interference, wherein said SU-MIMO OLLA offset and said
extra offset are updated in responsive to receipt of an ACK/NACK
message for a packet reported from said UE.
2. The method according to claim 1, further comprising:
maintaining, for each of transmission layers, a respective SU-MIMO
OLLA offset and extra offset.
3. The method according to claim 2, wherein updating said SU-MIMO
OLLA offset and said extra offset further comprises: in responsive
to determination that said UE operates in the SU-MIMO transmission
mode: determining whether said UE is configured with a single
transmission layer or multiple transmission layers; updating, in
responsive of determination that said UE is configured with a
single transmission layer, SU-MIMO OLLA offsets for all
transmission layers with which said UE is configured; and updating,
in responsive of determination that said UE is configured with
multiple transmission layers, the SU-MIMO OLLA offset for the
transmission layer on which said ACK/NACK message is reported.
4. The method according to claim 2, wherein updating said SU-MIMO
OLLA offset and said extra offset further comprises: in responsive
to determination that said UE operates in the MU-MIMO transmission
mode: determining whether said UE is configured with a single
transmission layer or multiple transmission layers; updating, in
responsive to determination that said UE is configured with a
single transmission layer, SU-MIMO OLLA offsets and extra offsets
for all transmission layers with which said UE is configured; and
updating, in responsive to determination that said UE is configured
with multiple transmission layers, the extra offset for the
transmission layer on which said ACK/NACK message is reported.
5. The method according to claim 1, wherein updating said SU-MIMO
OLLA offset and said extra offset further comprises: increasing, in
responsive to receipt of a ACK message reported from said UE, at
least one offset to be updated by a first update step size;
decreasing, in responsive to receipt of a NACK message reported
from said UE, at least one offset to be updated by a second update
step size.
6. The method according to claim 5, wherein said first and second
update step sizes D.sub.step.sub.--.sub.up and
D.sub.step.sub.--.sub.down meet the equation below:
D.sub.step.sub.--.sub.down=D.sub.step.sub.--.sub.up/(1/FER-1),
wherein FER denotes a predefined value of Frame Error Rate.
7. The method according to claim 1, further comprising: modifying
said extra offset with an index indicative of orthogonality of
co-scheduled UEs on a resource block.
8. The method according to claim 7, wherein: said index indicative
of orthogonality of co-scheduled UEs on a resource block is an
orthogonality index for beamforming vectors of the co-scheduled UEs
.gamma..sub.r, .gamma. r = 1 M - 1 m = 1 M - 1 V 0 , r V m , r 2 ,
##EQU00002## wherein M is the number of UEs co-scheduled on a same
recourse block; V.sub.0,r and V.sub.m,r are the normalized
beamforming weights of the r.sup.th layer of the concerned UE and
the m.sup.th co-scheduled UE on a resource block, respectively.
9. The method according to claim 6, further comprising: modifying
said extra offset with a constant scalar to ensure that said extra
offset is not greater than said SU-MIMO OLLA offset.
10. The method according to claim 9, wherein: said constant scalar
C.sub.scale is determined by C.sub.scale=M/T.sub.threshold, where M
is the number of co-scheduled UEs on the same resource block, and
T.sub.threshold is the threshold on the beamforming weight
correlation between two UEs.
11. The method according to claim 1, further comprising:
calculating an effective SINR based on OLLA-adjusted SINRs;
determining a modulation and coding scheme based on said effective
SINR.
12. An apparatus for link adaptation in a wireless communication
system, comprising: means for determining whether a UE operates in
a SU-MIMO transmission mode or in a MU-MIMO transmission mode;
means for applying, in responsive to determination that said UE
operates in the SU-MIMO transmission mode, a SU-MIMO OLLA offset to
a signal to interference and noise ratio adjusted with inner loop
link adaptation; means for applying, in responsive to determination
that said UE operates in the MU-MIMO transmission mode, a MU-MIMO
OLLA offset to a signal to interference and noise ratio adjusted
with inner loop link adaptation, wherein said MU-MIMO OLLA offset
is based on said SU-MIMO OLLA offset and an extra offset which is
indicative of inter-user interference, wherein said apparatus
further comprises means for updating said SU-MIMO OLLA offset and
said extra offset in responsive to receipt of an ACK/NACK message
for a packet reported from said UE.
13. The apparatus according to claim 12, further comprising: means
for maintaining, for each of transmission layers, a respective
SU-MIMO OLLA offset and extra offset.
14. The apparatus according to claim 13, wherein means for updating
said SU-MIMO OLLA offset and said extra offset is configured for:
in responsive to determination that said UE operates in the SU-MIMO
transmission mode: determining whether said UE is configured with a
single transmission layer or multiple transmission layers;
updating, in responsive of determination that said UE is configured
with a single transmission layer, SU-MIMO OLLA offsets for all
transmission layers with which said UE is configured; and updating,
in responsive of determination that said UE is configured with
multiple transmission layers, the SU-MIMO OLLA offset for the
transmission layer on which said ACK/NACK message is reported.
15. The apparatus according to claim 13, wherein means for updating
said SU-MIMO OLLA offset and said extra offset is configured for:
in responsive to determination that said UE operates in the MU-MIMO
transmission mode: determining whether said UE is configured with a
single transmission layer or multiple transmission layers;
updating, in responsive to determination that said UE is configured
with a single transmission layer, SU-MIMO OLLA offsets and extra
offsets for all transmission layers with which said UE is
configured; and updating, in responsive to determination that said
UE is configured with multiple transmission layers, the extra
offset for the transmission layer on which said ACK/NACK message is
reported.
16. The apparatus according to claim 12, wherein means for updating
said SU-MIMO OLLA offset and said extra offset is configured for:
increasing, in responsive to receipt of a ACK message reported from
said UE, at least one offset to be updated by a first update step
size; decreasing, in responsive to receipt of a NACK message
reported from said UE, at least one offset to be updated by a
second update step size.
17. The apparatus according to claim 16, wherein said first and
second update step sizes D.sub.step.sub.--.sub.up and
D.sub.step.sub.--.sub.down meet the equation below:
D.sub.step.sub.--.sub.down=D.sub.step.sub.--.sub.up/(1/FER-1),
wherein FER denotes a predefined value of Frame Error Rate.
18. The apparatus according to claim 12, further comprising: means
for modifying said extra offset with an index indicative of
orthogonality of co-scheduled UEs on a resource block.
19. The apparatus according to claim 18, wherein: said index
indicative of orthogonality of co-scheduled UEs on a resource block
is an orthogonality index for beamforming vectors of the
co-scheduled UEs .gamma..sub.r, .gamma. r = 1 M - 1 m = 1 M - 1 V 0
, r V m , r 2 , ##EQU00003## wherein M is the number of UEs
co-scheduled on a same recourse block; V.sub.0,r and V.sub.m,r are
the normalized beamforming weights of the r.sup.th layer of the
concerned UE and the m.sup.th co-scheduled UE on a resource block,
respectively.
20. The apparatus according to claim 17, further comprising: means
for modifying said extra offset with a constant scalar to ensure
that said extra offset is not greater than said SU-MIMO OLLA
offset.
21. The apparatus according to claim 20, wherein: said constant
scalar C.sub.scale is determined by C.sub.scale=M/T.sub.threshold,
where M is the number of co-scheduled UEs on the same resource
block, and T.sub.threshold is the threshold on the beamforming
weight correlation between two UEs.
22. The apparatus according to claim 12, further comprising: means
for calculating an effective SINR based on OLLA-adjusted SINRs;
means for determining a modulation and coding scheme based on said
effective SINR.
23. A base station in a wireless communication system, comprising:
at least one processor; and at least one memory including computer
program code, wherein the at least one memory and the computer
program code are configured to, with the at least one processor,
perform the method for link adaptation according to claim 11.
24. A wireless communication system, comprising a base station
according to claim 23.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to a communication
system, particularly to a method and apparatus for outer loop link
adaptation (OLLA) in a wireless communication system.
DESCRIPTION OF THE RELATED ART
[0002] The Third Generation Partnership Project (3GPP) Standard for
Long Term Evolution (LTE)/LTE-Advanced (LTE-A), also known as the
evolution standard of the great success of 3.sup.rd Generation
technology, is aiming at creating a new series of specifications
for the new evolving radio-access technology, which is able to
provide higher bandwidth, lower latency, and better quality of
service (QoS) guarantees.
[0003] In the cellular communication systems such as LTE/LTE-A
systems, adaptive modulation coding (AMC) technology is adopted to
suppress radio channel time variance. It is known that in so-called
inner loop link adaptation (as opposed to outer loop link
adaptation) methods, a quantized indication of channel quality such
as Channel Quality Indicator (CQI) is reported from a user
equipment (UE) to a corresponding base station such as an eNode B
(eNB). The eNB estimates signal to interference plus noise ratio
(SINR) of the UE based on the reported indication of channel
quality such as CQI. The eNB establishes a mapping relationship
between the levels of SINR and modulation and coding schemes (MSCs)
in advance. As such, the eNS can determine a proper MCS for the
uplink/downlink transmission of the UE by comparing the estimated
SINR with the predetermined thresholds of SINR.
[0004] However, the estimated SINR may not be accurate due to some
factors of un-modeled interferences and error, such as CQI
estimation errors, CQI report and process delay, etc. This results
in improper MCS selection, which then lowers down system spectrum
efficiency.
[0005] As an effective way to compensate for the above-mentioned
inaccuracy which may occur in the procedure of inner loop link
adaptation, so-called outer loop link adaptation (OLLA) is adopted
to add an offset to the estimated SINR. The OLLA offset is adjusted
based on information of UE-reported acknowledgement (ACK) or
non-acknowledgement (NACK) of transmitted packets. Accordingly, it
facilitates keeping accumulated frame error rate (FER) around a
predefined value. The MCS selection with OLLA-adjusted SINR is more
accurate and therefore the spectrum efficiency of the communication
system is improved.
[0006] Some wireless communication scenarios for example the
Transmission Mode 8 of LTE Releases 9 and 10 allow UEs to switch
dynamically between single-user multiple input multiple output
(SU-MIMO) transmission mode and multi-user multiple input multiple
output (MU-MIMO) transmission mode. Due to interlaced transmission
periods between SU-MIMO and MU-MIMO experienced by the UE, the
existing OLLA scheme cannot track the SINR offsets effectively for
both transmission modes. In addition, the varying inter-user
interferences are introduced in the MU-MIMO transmission mode by
dynamic UE pairing, which is, however, not considered in the
existing OLLA scheme.
[0007] Considering the facts as mentioned above, the existing OLLA
scheme is not effective in the scenarios which allow UEs to switch
between SU-MIMO and MU-MIMO transmission modes.
SUMMARY OF THE INVENTION
[0008] To solve the problems in the prior art, one or more method
and apparatus embodiments according to the present invention aim to
provide an OLLA scheme of a wireless communication system for the
application scenarios where hybrid SU-MIMO and MU-MIMO transmission
modes are supported and to provide more reliable MCS estimation and
improve the system throughout.
[0009] According to an aspect of the present invention, an
embodiment of the present invention provides a method for link
adaptation in a wireless communication system. The method
comprises: determining whether a UE operates in a SU-MIMO
transmission mode or in a MU-MIMO transmission mode; applying, in
responsive to determination that the UE operates in the SU-MIMO
transmission mode, a SU-MIMO OLLA offset to a signal to
interference and noise ratio adjusted with inner loop link
adaptation; applying, in responsive to determination that the UE
operates in the MU-MIMO transmission mode, a MU-MIMO OLLA offset to
a signal to interference and noise ratio adjusted with inner loop
link adaptation, wherein the MU-MIMO OLLA offset is based on the
SU-MIMO OLLA offset and an extra offset which is indicative of
inter-user interference, wherein the SU-MIMO OLLA offset and the
extra offset are updated in responsive to receipt of an ACK/NACK
message for a packet reported from the UE.
[0010] According to another aspect of the present invention, an
embodiment of the present invention provides an apparatus for link
adaptation in a wireless communication system. The apparatus
comprises: means for determining whether a UE operates in a SU-MIMO
transmission mode or in a MU-MIMO transmission mode; means for
applying, in responsive to determination that the UE operates in
the SU-MIMO transmission mode, a SU-MIMO OLLA offset to a signal to
interference and noise ratio adjusted with inner loop link
adaptation; means for applying, in responsive to determination that
the UE operates in the MU-MIMO transmission mode, a MU-MIMO OLLA
offset to a signal to interference and noise ratio adjusted with
inner loop link adaptation, wherein the MU-MIMO OLLA offset is
based on the SU-MIMO OLLA offset and an extra offset which is
indicative of inter-user interference, wherein the apparatus
further comprises means for updating the SU-MIMO OLLA offset and
the extra offset are in responsive to receipt of an ACK/NACK
message for a packet reported from the UE.
[0011] According to further aspect of the present invention, an
embodiment of the present invention provides a base station in a
wireless communication system performing the method for link
adaptation according to an embodiment of the present invention.
[0012] According to further aspect of the present invention, an
embodiment of the present invention provides a wireless
communication system comprising a base station according to an
embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Inventive features regarded as the characteristics of the
present invention are set forth in the appended claims. However,
the present invention, its implementation mode, other objectives,
features and advantages will be better understood through reading
the following detailed description on the exemplary embodiments
with reference to the accompanying drawings, where in the
drawings:
[0014] FIG. 1 illustrates a flow chart of a procedure of link
modulation and coding adaptation according to an embodiment of the
present invention;
[0015] FIG. 2 illustrates a flow chart of a method of outer loop
link adaptation according to an embodiment of the present
invention;
[0016] FIG. 3 schematically illustrates a block diagram of OLLA
offset generating module according to an embodiment of the present
invention;
[0017] FIG. 9 illustrates a flow chart of a procedure of updating
OLLA offsets according to an embodiment of the present invention;
and
[0018] FIG. 5 schematically illustrates a block diagram of an eNB
device according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings. In the
following description, many specific details are illustrated so as
to understand the present invention more comprehensively. However,
it is apparent to the skilled in the art that implementation of the
present invention may not have these details. Additionally, it
should be understood that the present invention is not limited to
the particular embodiments as introduced here. On the contrary, any
arbitrary combination of the following features and elements may be
considered to implement and practice the present invention,
regardless of whether they involve different embodiments. Thus, the
following aspects, features, embodiments and advantages are only
for illustrative purposes, and should not be understood as elements
or limitations of the appended claims, unless otherwise explicitly
specified in the claims.
[0020] FIG. 1 illustrates a flow chart of a procedure of link
modulation and coding adaptation according to an embodiment of the
present invention.
[0021] At step S100, the processing at an eNB for link modulation
and coding adaptation starts.
[0022] At step S110, a UE-specific SINR for each of RBs assigned to
a UE is estimated based on a quantized indication of channel
quality such as CQI reported from a UE.
[0023] In the cellular communication systems with MIMO
technologies, multiple antennas are used at both the transmitter
and receiver. Spatial multiplexing results in increased data rate
in bandwidth limited scenarios by creating several parallel
"channels" between the transmitting antennas and the receiving
antennas. The term "layer" or "transmission layer" refers to each
of channels between the transmitting antennas and the receiving
antennas. And the term "stream" or "data stream" refers to data
transmitted on a transmission layer. In particular, in the MU-MIMO
transmission mode, multiple users can share the parallel
transmission layers on the same time-frequency resource by
combining the spatial properties with the appropriate interference
suppressing and receiver processing in order to improve the overall
cell capacity.
[0024] At step S120, the estimated SINR is adjusted with inner loop
link adaptation.
[0025] There are various algorithms of inner loop link adaptation
in the art, some of which have been prevailed in the field and some
of which may be developed for future use, etc. It is appreciated
that the OLLA scheme according to the embodiments of the present
invention can be used in conjunction with any kind of inner loop
link adaptation without any limitation.
[0026] At step S130, a procedure of the outer link loop adaptation
according to an embodiment of the present invention is performed,
to obtain OLLA-adjusted SINR for each of transmission layers.
[0027] As discussed previously, some wireless communication
scenarios for example Transmission Mode 8 of LTE Releases 9 and 10
allow UEs to switch dynamically between the SU-MIMO transmission
mode and the MU-MIMO transmission mode. In the outer link loop
adaptation scheme according to an embodiment of the present
invention, separate OLLA offsets for the SU-MIMO and MU-MIMO
transmission modes are adopted to track the SINR offsets
effectively for both transmission modes. In the outer link loop
adaptation scheme according to an embodiment of the present
invention, it is proposed that a MU-MIMO OLLA offset for a
transmission layer is based on the SU-MIMO OLLA offset for the
transmission layer and an extra offset which is indicative of
inter-user interference; and ACK/NACK messages for SU and MU
packets are used to trigger OLLA offset updating procedure. The
detailed procedure of OLLA according to embodiments of the present
invention will be set forth with reference to FIGS. 2-4.
[0028] At step S140, an effective SINR per layer is calculated
based on the OLLA-adjusted SINRs.
[0029] In the cellular communication systems, the eNB assigns
resource blocks (RB) to UEs. A RB refers to a group of subcarriers
over one subframe. And each UE can be assigned with multiple RBs
for transmission. The eNB needs to determine the number of
transmission layers of the UE and an effective SINR per layer.
[0030] The OLLA offset of SINR is applied before getting the
effective SINR according to an embodiment of the present invention.
On different RBs assigned to a UE, the UE might have different
paring UEs. According to the strength of the inter-user
interference, a different OLLA offsets depending on different
paring manners can be applied to the SINR of the RB and then these
OLLA-adjusted SINRs of the assigned RBs can be mapped into an
effective SINR. Those skilled in the art may appreciate that it
will be advantageous that the effective SINR is calculated taken
into UEs' pairing matters in the MU-MIMO transmission mode.
[0031] At step S150, the calculated effective SINR is passed into
the MCS look up table to find a suitable MCS for transmission.
[0032] At step S160, the processing ends.
[0033] FIG. 2 illustrates a flow chart of a method of outer loop
link adaptation according to an embodiment of the present
invention.
[0034] At step S210, it is determined whether the UE operates in a
SU-MIMO transmission mode or in a MU-MIMO transmission mode.
[0035] At step S220, if it is determined that the UE operates in
the SU-MIMO transmission mode, a SU-MIMO OLLA offset is applied to
the SINR adjusted with inner loop link adaptation.
[0036] At step S230, if it is determined that UE operates in the
MU-MIMO transmission mode, a MU-MIMO OLLA offset is applied to the
SINR adjusted with inner loop link adaptation.
[0037] The SU-MIMO OLLA offset and MU-MIMO OLLA offset are
determined by an OLLA offset generating module, wherein the MU-MIMO
OLLA offset is determined based on the SU-MIMO OLLA offset and an
extra offset which is indicative of inter-user interference and the
SU-MIMO OLLA offset and the extra offset are updated in responsive
to receipt of an ACK/NACK message for a packet reported from said
UE. The functionality of the OLLA offset generating module will be
discussed in details in conjunction with FIG. 3.
[0038] FIG. 3 schematically illustrates a block diagram of OLLA
offset generating module according to an embodiment of the present
invention.
[0039] As shown in FIG. 3, reference numeral 300 denotes an OLLA
offset generating module, which comprises an OLLA update unit 310,
an OLLA memory unit 320 and an OLLA output unit 330.
[0040] The OLLA memory unit 320 is used to maintain parameters and
values used to generate OLLA offsets. According to an embodiment of
the present invention, the OLLA memory unit 320 maintains, for each
of transmission layers, a respective SU-MIMO OLLA offset, which can
be referred to as .beta..sub.r, r=0, 1, 2, . . . , L, and a
respective extra offset, which can be referred to as .alpha..sub.r,
r=0, 1, 2, . . . , L, wherein L is supported max number of
transmission layers based on the UE capacity and the eNB
configuration. Specifically, .beta..sub.0 is the SU-MIMO OLLA
offset for single-layer transmission, while .beta..sub.r, r=1, 2, .
. . , L, is the SU-MIMO OLLA offset for the corresponding r.sup.th
transmission layer when there are multiple layers. Similarly,
.alpha..sub.0 is the extra offset of MU-MIMO transmission mode for
single-layer transmission, while .alpha..sub.r, r=1, 2, . . . , L,
is the extra offset for the corresponding r.sup.th transmission
layer when there are multiple layers.
[0041] According to an embodiment of the present invention, the
OLLA memory unit 320 may maintain parameters which are utilized by
the other units. In an exemplary implementation, the OLLA memory
unit 320 may maintain the step sizes D.sub.step.sub.--.sub.up and
D.sub.step.sub.--.sub.down for increasing and decrementing the OLLA
offsets in the OLLA update unit 310. D.sub.step.sub.--.sub.up and
D.sub.step.sub.--.sub.down may be constant or adaptive in
responsive to the accumulated FER. In another exemplary
implementation, the OLLA memory unit 320 may maintain a constant
scalar C.sub.scale, which is utilized by the OLLA output unit 330
to adjust the weight of the extra offset in the outputted MU-MIMO
OLLA offset and will be discussed below.
[0042] The OLLA update unit 310 is used to update the SU-MIMO OLLA
offset and the extra offset in responsive to receipt of an ACK/NACK
message for a packet reported from a UE. Specifically, the OLLA
update unit 310 updates a SU-MIMO OLLA offset .beta..sub.r, r=0, 1,
2, . . . , L, and a extra offset .alpha..sub.r, r=0, 1, 2, . . . ,
L, in responsive to an ACK/NACK message.
[0043] Now, reference is made to FIG. 4 to set forth an exemplary
procedure performed by the OLLA update unit 310 according to a
preferred embodiment of the present invention.
[0044] As shown in FIG. 4, at step S400, the processing starts.
[0045] At step S410, an ACK/NACK message for a packet from a UE is
received at the eNB.
[0046] At step S420, it is determined whether the UE sending the
ACK/NACK message operates in the SU-MIMO transmission mode or in
the MU-MIMO transmission mode.
[0047] In an exemplary implementation, the determination can be
performed in such a matter that the eNB keeps records of whether
packets are in the SU-MIMO transmission mode or in the MU-MIMO
transmission mode and when the ACK/NACK for a packet is received,
the eNB can make the determination and then carry out corresponding
OLLA offset update steps.
[0048] If it is determined at step S420 that the UE operates in the
SU-MIMO transmission mode, the processing proceeds with steps
S430-S434.
[0049] At step 430, it is determined whether the UE is configured
with a single-layer or multiple layers.
[0050] If it is determined that the US is configured with a single
transmission layer, at steps S431 and S432, SU-MIMO OLLA offsets
for all transmission layers with which said UE is configured are
updated. Specifically, at step S431, in responsive to receipt of an
ACK message of a packet from the UE, the SU-MIMO OLLA offsets for
all transmission layers, i.e., .beta..sub.r, r=0, 1, 2, . . . , L,
which are maintained in the OLLA memory unit 320, are increased by
D.sub.step.sub.--.sub.up. At step S432, in responsive to receipt of
a NACK message of a packet from the UE, the SU-MIMO OLLA offsets
for all transmission layers, i.e., .beta..sub.r, r=0, 1, 2, . . . ,
L, which are maintained in the OLLA memory unit 320, are decreased
by D.sub.step.sub.--.sub.down.
[0051] If it is determined that the UE is configured with multiple
transmission layers, at steps S433 and S434, only the SU-MIMO OLLA
offset for the transmission layer on which the ACK/NACK message is
reported is updated. Specifically, at step S433, in responsive to
receipt of an ACK message of a packet from the UE, the SU-MIMO OLLA
offset for the transmission layer on which the ACK message is
reported, i.e., .beta..sub.r, r.epsilon.R, R={r: r.sup.th-layer is
ACKed}, which is maintained in the OLLA memory unit 320, is
increased by D.sub.step.sub.--.sub.up. At Step S434, in responsive
to receipt of a NACK message of a packet from the UE, the SU-MIMO
OLLA offset for the transmission layer on which the NACK message is
reported, i.e., .beta..sub.r, r.epsilon.S, S={r:r.sup.th-layer is
NACKed}, which is maintained in the OLLA memory unit 320, is
decreased by D.sub.step.sub.--.sub.down.
[0052] If it is determined at step S420 the UE operates in the
MU-MIMO transmission mode, the processing proceeds with steps
S440-S449.
[0053] At step 940, it is determined whether the UE is configured
with a single-layer or multiple layers.
[0054] If it is determined that the UE is configured with a single
transmission layer, at steps S441 and S442, SU-MIMO OLLA offsets
and extra offsets for all transmission layers with which said UE is
configured are updated. Specifically, at step S441, in responsive
to receipt of an ACK message of a packet from the UE, the SU-MIMO
OLLA offsets for all transmission layers, i.e., .beta..sub.r, r=0,
1, 2, . . . , L, and the extra offsets for all transmission layers,
i.e., .alpha..sub.r, r=0, 1, 2, . . . , L, which are maintained in
the OLLA memory unit 320, are all increased by
D.sub.step.sub.--.sub.up. At step S442, in responsive to receipt of
a NACK message of a packet from the UE, the SU-MIMO OLLA offsets
for all transmission layers, i.e., .beta..sub.r, r=0, 1, 2, . . . ,
L, and the extra offsets for all transmission layers, i.e.,
.alpha..sub.r, r=0, 1, 2, . . . , L, which are maintained in the
OLLA memory unit 320, are all decreased by
D.sub.step.sub.--.sub.down.
[0055] If it is determined that the UE is configured with multiple
transmission layers, at steps S993 and S5999, only the extra offset
for the transmission layer on which the ACK/NACK message is
reported is updated. Specifically, at step S443, in responsive to
receipt of an ACK message of a packet from the UE, the extra offset
for the transmission layer on which the ACK message is reported,
i.e., .alpha..sub.r, r.epsilon.R, R={r: r.sup.th-layer is ACKed},
which is maintained in the OLLA memory unit 320, is increased by
D.sub.step.sub.--.sub.up. At Step S444, in responsive to receipt of
a NACK message of a packet from the UE, the extra offset for the
transmission layer on which the NACK message is reported, i.e.,
.alpha..sub.r, r.epsilon.S, S={r: r.sup.th-layer is NACKed}, which
is maintained in the OLLA memory unit 320, is decreased by
D.sub.step.sub.--.sub.down.
[0056] At step S450, the processing ends.
[0057] The update step sizes D.sub.step.sub.--.sub.up and
D.sub.step.sub.--.sub.down can be predefined and maintained in the
OLLA Memory unit 320. According to an alternative implementation of
the embodiment of the present invention, The update step sizes
D.sub.step.sub.--.sub.up and D.sub.step.sub.--.sub.down is defined
to meet following equation:
D.sub.step.sub.--.sub.down=D.sub.step.sub.--.sub.up/(1/FER-1),
[0058] wherein FER denotes a predefined value of Frame Error
Rate.
[0059] According to the update procedure as shown in FIG. 4, it can
be noted that for transmission with multiple layers, only those
offset corresponding to those specific layers are updated, while
for single-layer transmission, offsets for all of the transmission
layers are updated. The reason for doing so is that although only a
single layer is configured of the concerned UE during single layer
transmission, the fluctuations of the time varying channel
experienced by the UE on this layer are also true to all of the
layers if there are multiple layers configured. As such, the
procedure helps the eNB to keep the OLLA offsets for multiple
layers correctly tracking the channel condition during single layer
transmissions, which is important for the OLLA effectiveness.
[0060] Furthermore, according to the update procedure as shown in
FIG. 4, it can also be noted that in the single-layer transmission
case, for an ACK/NACK message of the SU-MIMO packets, the SU-MIMO
OLLA offsets for all transmission layers, i.e., .beta..sub.r, r=0,
1, 2, . . . , L, are updated, while for an ACK/NACK massage of the
MU-MIMO packets, both the SU-MIMO OLLA offsets for all transmission
layers, i.e., .beta..sub.r, r=0, 1, 2, . . . , L, and the extra
offsets for all transmission layers, i.e., .alpha..sub.r, r=0, 1,
2, . . . , L, are updated. As such, during the interlaced
transmission periods between SU-MIMO and MU-MIMO transmission
modes, even if the UE currently operates in MU-MIMO transmission
mode, the eNB is able to update the SU-MIMO OLLA offsets based on
ACK/NACK message of the MU-MIMO packets. Therefore the OLLA offsets
for SU-MIMO can still track the channel fluctuations even during
MU-MIMO transmission period. This is especially important for quick
convergence of the OLLA offsets when a UE switches from MU-MIMO
transmission mode to SU-MIMO transmission mode.
[0061] Returning now to FIG. 3, the OLLA output unit 330 generates
OLLA offsets (dB) used in the SU-MIMO and MU-MIMO transmission
modes based on the OLLA offset values and parameters maintained in
the OLLA memory unit 320, wherein the SU-MIMO OLLA offset
.delta..sub.0.sup.SU for the single transmission layer can be
denoted as:
.delta..sub.0.sup.SU=.beta..sub.0, 1)
[0062] the SU-MIMO OLLA offset .delta..sub.r.sup.SU for the
corresponding r.sup.th transmission layer, when there are multiple
layers, can be denoted as:
.delta..sub.r.sup.SU=.beta..sub.r, r=1,2, . . . ,L; 2)
[0063] the MU-MIMO OLLA offset .delta..sub.0.sup.MU for the single
transmission layer can be denoted as:
.delta..sub.0.sup.MU=.alpha..sub.0+.beta..sub.0; 3)
[0064] the MU-MIMO OLLA offset .delta..sub.r.sup.MU for the
corresponding r.sup.th transmission layer, when there are multiple
layers, can be denoted as:
.delta..sub.r.sup.MU=.alpha..sub.r+.beta..sub.r, r=1,2, . . . ,L,
4)
[0065] wherein L is supported max number of transmission layers
based on the UE capacity and the eNB configuration.
[0066] For the purpose of simplicity, equations 1) and 2) can be
combined and denoted as:
.delta..sub.r.sup.SU=.beta..sub.r, r=1,2, . . . ,L; 5)
[0067] and
[0068] equations 3) and 4) can be combined and denoted as:
.delta..sub.r.sup.MU.alpha..sub.r+.beta..sub.r, r=0,1,2, . . . ,L,
6)
[0069] In a preferred embodiment of the present invention, the OLLA
output unit 330 can determine the MU-MIMO OLLA offset for
corresponding transmission layer by modifying the extra offset with
an index indicative of orthogonality of co-scheduled UEs on a RB.
For example, an orthogonality index for beamforming vectors of the
co-scheduled UEs .gamma..sub.r can be introduced to modify the
extra offset .alpha..sub.r, so that the modified MU-MIMO OLLA
offset may reflect the varying inter-user interference caused by
dynamic UE pairing in the MU-MIMO transmission mode.
[0070] Preferably, the extra offset may be further modified with a
constant scalar to ensure that the extra offset is not greater than
the SU-MIMO OLLA offset.
[0071] According to the preferred embodiment, the equation 6) can
be optimized as
.delta..sub.r.sup.MU=C.sub.scale.gamma..sub.r.alpha..sub.r.beta..sub.r,
r=0,1,2, . . . ,L, 7)
[0072] wherein L is supported max number of transmission layers
based on the UE capacity and the eNB configuration; .gamma..sub.r
is an orthogonality index for the beamforming vectors of the
co-scheduled UE, which can be used as a strength measurement of
inter-user interference; C.sub.scale is a constant scalar such that
0<C.sub.scale.gamma..sub.r.ltoreq.1.
[0073] In an exemplary implementation of the preferred embodiment
of the present invention, .gamma..sub.r can be provided to the OLLA
output unit 330 by a UE pairing module in the eNB, such as the
scheduler of the eNB.
[0074] Suppose there are M UEs co-scheduled on the same RB, then
for the concerned UE,
.gamma. r = 1 M - 1 m = 1 M - 1 V 0 , r V m , r 2 , 8 )
##EQU00001##
[0075] wherein V.sub.0,r and V.sub.m,r are the normalized
beamforming weights of the r.sup.th layer of the concerned UE and
the m.sup.th co-scheduled UE on a RB, respectively. It is
appreciated that RB index is omitted here, for the purpose of
simplicity.
[0076] In an exemplary implantation of the preferred embodiment of
the present invention, C.sub.scale can be chosen in advance and
maintained in the OLLA memory unit 320. For example, C.sub.scale
can be chosen to meet following equation:
C.sub.scale=M/T.sub.threshold 9)
[0077] where M is the number of co-scheduled UEs on the same
resource, and T.sub.threshold is the threshold on the beamforming
weight correlation between two UEs.
[0078] Only if
.parallel.V.sub.i,rV.sub.j,r.parallel..sup.2<Threshold, then UE
i and UE j will be co-scheduled on the same RB. Thus the max value
of .gamma..sub.r is T.sub.threshold. M is to account for the power
split between the M co-scheduled UEs.
[0079] For example, in Transmission Mode 8 of LTE Release 9, it is
specified that M=2, T.sub.threshold=0.3. Therefore,
C.sub.scale=2/0.3=6.67. In this example, It can be seen that
C.sub.scale is chosen for following reasons:
[0080] 1. V.sub.1,r and V.sub.1,r are first normalized and a BF
correlation threshold 0.3 is used to rule out UEs whose BF weights
are not orthogonal enough; and
[0081] 2. then V.sub.0,r and V.sub.1,r are scaled by 1/sqrt(2) to
account for power split between the two co-scheduled MU-MIMO
UEs.
[0082] Those skilled in the art may appreciate that the preferred
embodiments of the present invention as described above are only
intended to provide non-limiting examples to illustrate how to
optimize the MU-MIMO OLLA offset by modifying the extra offset.
However, depending on practical use, those skilled in the art may
choose one or more optimal scaling factors other than the
above-described ones to optimize the extra offset, or even choose
not to use any optimal scaling factors at all. Consequently, the
features described in the preferred embodiments of the present
invention should be regarded as being not indispensable but
alternative and/or preferable to the overall solution.
[0083] FIG. 5 schematically illustrates a block diagram of an eNB
device according to an embodiment of the present invention,
[0084] As shown in FIG. 5, reference numeral 500 denotes an eNB
device according to an embodiment of the present invention. The eNB
device comprises an inner loop link adaptation (ILLA) module 510,
an outer loop link adaptation (OLLA) module 520, a modulation and
coding module 530, and a scheduling module 540.
[0085] The ILLA module 510 is configured to perform estimation of
UE-specific SINR for each of RBs assigned to a UE, based on a
quantized indication of channel quality such as CQI reported from a
UE. The ILLA module 510 performs inner loop link adaptation to
adjust the estimated SINR.
[0086] The OLLA module 520 is configured to perform outer loop link
adaptation according to embodiments of the present invention, to
obtain OLLA-adjusted SINR for each of transmission layers. An
exemplary operation of the OLLA module 520 is depicted in FIG. 2.
The OLLA module 520 determines whether the UE operates in a SU-MIMO
transmission mode or in a MU-MIMO transmission mode. Depending on
the result of determination, the OLLA module 520 applies a SU-MIMO
OLLA offset or a MU-MIMO OLLA offset generated by the OLLA offset
generating module 300 to the SINR adjusted by the ILLA module 510,
respectively.
[0087] The OLLA offset generating module 300 of exemplary
embodiments of the present invention has been described above in
connection with FIG. 3. In the OLLA offset generating module 300,
the MU-MIMO OLLA offset .delta..sub.r.sup.MU is determined based on
the SU-MIMO OLLA offset .delta..sub.r.sup.SU=.beta..sub.r and an
extra offset .alpha..sub.r which is indicative of inter-user
interference and the SU-MIMO OLLA offset .beta..sub.r and the extra
offset .alpha..sub.r are updated in responsive to receipt of an
ACK/NACK message for a packet reported from said UE, for example,
according to the processing illustrated in FIG. 4. According to a
preferred embodiment of the present invention, the extra offset
.alpha..sub.r can be modified with an index indicative of
orthogonality of co-scheduled UEs on a RB. As an example, an
orthogonality index for beamforming vectors of the co-scheduled UE
.gamma..sub.r can be provided from the scheduling module 540 to the
OLLA offset generating module 300 of the OLLA module 520 to modify
the extra offset .alpha..sub.r. Preferably, the extra offset a, may
further modified with a constant scalar to ensure that the extra
offset is not greater than the SU-MIMO OLLA offset. Therefore,
according to the preferred embodiment, the MU-MIMO OLLA offset
.delta..sub.r.sup.MU for corresponding transmission layer can be
denoted as
.delta..sub.r.sup.MU=C.sub.scale.gamma..sub.r.alpha..sub.r+.beta..sub.r,
r=0,1,2, . . . ,L,
[0088] wherein L is supported max number of transmission layers
based on the UE capacity and the eNB configuration; .gamma..sub.r
is an orthogonality index for the beamforming vectors of the
co-scheduled UE, which can be used as a strength measurement of
inter-user interference; C.sub.scale is a constant scalar such that
0<C.sub.scale.gamma..sub.r.ltoreq.1.
[0089] The ILLA module 510 is configured to calculate an effective
SINR based on OLLA-adjusted SINRs from the OLLA module 520. Then, a
suitable MCS for transmission can be determined from a MCS lookup
table and used in the modulation and coding module 530.
[0090] Here, the eNB device 500 is described with the modules or
components which are most relevant to the embodiments of the
present invention. However, those skilled in the art can appreciate
that the eNB device 500 also comprises other modules and components
for performing the functionality of cellular communication,
including antennas; transceiver (having a transmitter (TX) and a
receiver (RX)); processors such as one or more of general purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs) and processors based on multi-core
processor architecture; memory module be of any type suitable to
the local technical environment and may be implemented using any
suitable data storage technology; etc. Those modules or components
are well known in the art and the description thereof is omitted
for the purpose of conciseness.
[0091] A link adaptation processing in an eNB according to an
embodiment of the present invention has been depicted in detail
with reference to FIGS. 1, 2 and 4. It should be noted that the
above depiction is only exemplary, not intended for limiting the
present invention. In other embodiments of the present invention,
this method may have more, or less, or different steps, and
numbering the steps is only for making the depiction more concise
and much clearer, but not for stringently limiting the sequence
between each steps, while the sequence of steps may be different
from the depiction. For example, in some embodiments, the above one
or more optional steps may be omitted. Specific embodiment of each
step may be different from the depiction. All these variations fall
within the spirit and scope of the present invention.
[0092] In general, the various exemplary embodiments may be
implemented in hardware or special purpose circuits, software,
logic or any combination thereof. For example, some aspects may be
implemented in hardware, while other aspects may be implemented in
firmware or software which may be executed by a controller,
microprocessor or other computing device, although the invention is
not limited thereto. While various aspects of the exemplary
embodiments of this invention may be illustrated and described as
block and signaling diagrams, it is well understood that these
blocks, apparatus, systems, techniques or methods described herein
may be implemented in, as non-limiting examples, hardware,
software, firmware, special purpose circuits or logic, general
purpose hardware or controller or other computing devices, or some
combination thereof.
[0093] As such, it should be appreciated that at least some aspects
of the exemplary embodiments of the inventions may be practiced in
various components such as integrated circuit chips and modules. As
well known in the art, the design of integrated circuits is by and
large a highly automated process.
[0094] The present invention may also be embodied in the computer
program product which comprises all features capable of
implementing the method as depicted herein and may implement the
method when loaded to the computer system.
[0095] The present invention has been specifically illustrated and
explained with reference to the preferred embodiments. The skilled
in the art should understand various changes thereto in form and
details may be made without departing from the spirit and scope of
the present invention.
* * * * *